This invention relates to apparatus for the networking of personal computers and workstations, for the purpose of sharing access to and usage of computer programs and files, particularly those of the multimedia type, in a cost effective manner.
Said personal computers and workstations are computers intended for use on, or in close proximity to, the user input/output devices, such as a keyboard, computer mouse and video display screen that are typically located on an individual user's desktop. Disclosed herein is computer interconnection apparatus that is adapted to permit deploying the user input/output components of said personal computers and workstations at a desktop location remote from the physical location of said personal computers and their associated programs and files. The disclosed apparatus permits a plurality of users at different remote locations to use said personal computer apparatus on a shared basis. Said remotely located user apparatus is referred to herein as workstation terminals, or workstations.
Multimedia computer programs are those that display on the user's video display monitor, text type information, computer generated graphical information, and all types of picture image type information. Including full color, still and animated line drawings, photograph quality still pictures, and full motion moving pictures. Multimedia programs are also capable of delivering high fidelity, stereo sound to said user terminal.
Local Area Networks (LAN's ) are data communications networks that provide data paths among personal computers or workstations that are localized to a single building, or to a numerically small and physically close, group of buildings. Computer networks that are comprised of an interconnected set of LAN's within a specific area, such as an industrial park, a residential network of public schools, a university campus, or a small urban community, are typically referred to in the art as Metropolitan Area Networks or MANS. The network apparatus described herein is of the metropolitan area type in that it is intended to permit the interconnection of personal computers or workstations to remotely located user-operable input/output devices (i.e. keyboard, mouse and display tube) throughout a metropolitan area. Typically, computer networks need to serve workstations that use different computer operating systems, such as Microsoft MS-DOS workstations (Microsoft and MS-DOS are registered trademarks of the Microsoft Corporation), IBM OS/2 workstations (IBM and OS/2 are registered trademarks of International Business Machines Corporation), and Apple Macintosh workstations (Apple and Macintosh are registered trademarks of Apple Computer, Inc.).
There are three advantages to operating multimedia computing in a network environment compared with an individual workstation environment. The first is software cost savings. Multimedia software packages and associated files are expensive. Networkable versions of said software can often be purchased at considerable cost savings when compared with the purchase of individual workstation copies. The second advantage is hardware savings. With a multimedia network it is possible to maintain all source software and associated program data at one location only. Without such a network, each workstation operates individually in a non-network environment thus requiring each workstation to have its own CD ROM apparatus for storage of the source software and associated program data. Accordingly, with a multimedia network, the larger the number of workstations on the network the greater the software and hardware savings. The third advantage is software security a centralized network controller that is accessible over the network to users of workstations attached to the network, can incorporate security features to ensure that files are protected from unauthorized users. Additional economies may be had through the use of diskless workstations for network users. Moreover use of diskless workstations prevents program data and software file data from being downloaded to disks for unauthorized copying. Diskless workstations also keep the computing environment healthy as users cannot enter personal files at the workstation. Said user files being potentially infected by system crippling computer sabotage known as software viruses.
One important application of multimedia computing is the education system. Educators wish to take advantage of the opportunities that multimedia computer assisted teaching offers. However educational budgets are a limited resource. In order to reduce the cost of a multimedia installation it would be advantageous if a plurality of schools, and a plurality of classrooms and other locations within said schools, could access a central source of multimedia files.
It would also be advantageous if the workstation terminal, could be at a cost lower than that of a personal computer. Personal computers useful for multimedia type computer assisted instruction are expensive due to the requirement for fast processing speed and their requirement to drive high resolution video display monitors.
Educators need to be able to economically upgrade their workstation apparatus as the art advances. The more expensive the workstation the more difficult it is for educators, or other multimedia network operators, to afford a multimedia network and the more difficult it is for said network operators to keep an installed network technologically current and therefore compatible with the latest multimedia software.
Prior art that addresses the need for low cost workstations remotely located from the computer apparatus, utilizes non-intelligent terminals connected to the computer via telephone cable and communications modems. Such art is not suitable in a multimedia environment due to the low data transmission speeds. High resolution, full color, full motion moving pictures require data rates of 200 Mb/s or greater, or 45 Mb/s or higher should the latest video compression apparatus be incorporated.
There is a need for the said multimedia system to be comprised of a network to serve user locations up to 7 kilometers from the central file server location. For example should said file server be located in a secondary school (or high school) said secondary school could serve nearby primary schools and junior high schools.
Prior art that extends MAN operating distance by the use of fiber optics could meet the distance requirements and perhaps provide adequate video quality. One example of which is the Fiber Distributed Data Interface, or FDDI, (FDDI operates at 100 Mb/s). But said art would be more expensive than the invention embodied herein as said art makes no provision for simplified multimedia workstations. FDDI is a fiber optic system standard approved by the International Organization for Standards and the American National Standards Institute.
There is a need for the remotely located multimedia workstations to operate with a performance effectively equivalent to workstations located adjacent to the file server that is user indistinguishable with respect to, video picture quality, data file access speed, and input keyboard and mouse response speed.
Mice and keyboard apparatus are designed and manufactured to be positioned within a few meters of the personal computer that they are connected to. Should such apparatus be moved several kilometers from said computers then the transmission link connecting said apparatus to said computers must meet the timing requirements of the original design. One example of such a mouse/keyboard input apparatus is the Apple Macintosh ADB (Apple Desktop Bus) system (Apple Desktop Bus is a registered trademark of Apple Computer, Inc.). The ADB Bus apparatus uses a polling scheme to interrogate such bus connected devices as a mouse and a keyboard. A mouse movement for example, causes the mouse apparatus to process and store movement information until such time as the ADB bus apparatus requests that the data be transferred from the mouse apparatus to the computer apparatus. The maximum time permitted from the time the computer sends a data request demand to a device and the device is required to respond is 260 micro-seconds for the ADB bus apparatus. Should said ADB bus system interface a computer with said mice/keyboard apparatus located several kilometers apart, said transmission link is required to be sufficiently fast that said timing requirements are met.
There is a need for the previously said plurality of remotely located low cost workstations to share access to and use of a lesser number of centrally located personal computer apparatus. Said shared usage network requires some kind of communication and control apparatus so that said remote user can initiate the connection of said low-cost workstation to one of said personal computers.
The invention embodied herein uses the public telephone system for initiating workstation connections. The advantages of using the public switched telephone network are that connection times are short to establish the workstation link on the network thus permitting one telephone circuit to service a large plurality of users. The telephone network is inexpensive and already in place, and the art of decoding dual-tone multiple frequency telephone signals is well known. One example of prior art that uses the public telephone system to permit the user to control centrally located non-telephone company equipment is: Bradley, Stretten, Stretten, and Wentzel (U.S. Pat. No. 4,878,245).
The general object of this invention is to provide a low cost, high quality, network of remote workstations which provide a plurality of users with access to and use of a centralized data base of multimedia computer files and programs.
It is an object of this invention that said remote workstations shall be able to be located up to 7 kilometers distant from said centrally located data base. The transmission system connecting said workstations to said central data base must be capable of delivering video quality to any remote workstation equal in quality to that viewed on any monitor located at the central data base location. Said monitors being of the type suitable for multimedia applications, that is being capable of displaying photograph quality color images. Said monitors would typically, be of the RGB type, be capable of displaying 1024.times.768 dots of resolution, have a video bandwidth of up to 3.2 MHz for each of the three RGB signals, have a horizontal scan rate of up to 35 KHz, and have a vertical scan rate up to 70 Hz.
It is a further object of this invention that the said workstation terminals be of a cost lower than that typical of personal computer workstations capable of the high quality of color video performance specified in the previously said objective.
It is an object of this invention that the transmission system connecting said remote workstations to said central data base be capable of providing an input response time that is user indistinguishable from that provided by a similar user operated workstation located at the central data base location. For both said remote workstations and said centrally located workstations said users will perceive no operational degrading delay with respect to both user generated keyboard inputs and user generated mouse inputs. The maximum permitted time from input device interrogation until the reception of the response shall be a maximum of 50% of the time that the Apple Computer ADB bus system permits, or 130 mseconds. The two way transmission time for a 7 kilometer glass fiber transmission line link between a central file server location and a remote workstation location is about 70 mseconds. This leaves a margin of about 60 mseconds for ADB bus and mouse response time, and auxiliary electronic delays at both ends of the transmission line. Therefore the electronic apparatus that interfaces the computing equipment at each end of the transmission line, for both directions of transmission, should not introduce more than 10 mseconds of delay each.
It is an object of this invention that the transmission system will support high fidelity, stereo audio signals. High fidelity being defined as an audio signal with a 3 dB power bandwidth from 50 to 15 KHz.
It is a further object of this invention that the transmission system will provide an Electronic Industries Association (EIA) RS232C compatible communication channel between the centrally located personal computers and the remotely located workstations for most printers, plotters and other such terminal devices.